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Monitoring and observation services
In Earth Sciences, regular observations over long periods of time are an essential support mechanism for research and also a response to contractual commitments to the State. They are necessary to understand the fundamental mechanisms that control the functioning of natural systems, to predict possible changes at different time scales and, as far as possible, to build predictive models.
Ensuring the sustainability of Earth and Universe Science observation facilities over long periods of time (several decades) is the role of the Observatories of Universe Sciences (OSU), including the Grenoble Observatory of Universe Sciences (OSUG).
– More information on the OSUG website
For OSUG, the ISTerre laboratory is responsible for the observation services dedicated to the Internal Earth. We manage and develop the alpine part of the national observation networks in seismology, geodesy and slope instabilities; we distribute and analyse the data. In addition, we have national responsibilities for coordinating some of these networks, and are responsible for the archiving and distribution node for French seismological data.
**Why?
The Western Alps are subject to moderate seismic activity. Every year, several hundred earthquakes are recorded and located there. Earthquakes strong enough to be felt are on average about twenty each year, the magnitude level reached by the strongest fortunately only rarely exceeding the value 5 (Le Grand-Bornand - Haute-Savoie, 5.1 on 14/12/1994; Annecy - Haute-Savoie, 5.3 on 15/07/1996). A very destructive earthquake, of magnitude 6 or more, is virtually possible at any point in the Western Alps and Provence.
This persistent seismic activity shows that the Alps are still an active mountain range, linked to the collision between the Eurasian plate to the north and west and the Adria plate to the southeast. To analyse the surface deformations associated with the evolution of the Alpine chain, ISTerre has been recording high-precision geodetic data (ground motion speeds) for nearly 20 years using GNSS satellite positioning systems. The analysis of this long series of data has just led to a paradoxical result. While horizontal movements at the limits of the Western Alps (between Lyon and Turin) are below the detectability threshold, the Internal Alps (including the Mont Blanc region) rise at a speed of nearly 2 mm per year.
Gravitational instabilities have a strong societal impact in a mountain region like the Alps, whose development they can hinder. Understanding these instabilities and predicting their onset is therefore a major research challenge. The diversity and complexity of the mechanisms for initiating, triggering and propagating slope movements, and their sensitivity to external forcing (earthquake rains, climate) require continuous, spatialized and multi-source observation of the slip.
**How?
ISTerre’s observation activities are integrated with the national observation services (SNO) of theCNRS-INSU in seismology, geodesy-gravimetry and slope instabilities (see organization chart below).
Within its geophysical data processing, archiving and distribution service, ISTerre hosts 3 components of the National Project Information SystemRESIF, including the French node of the European Seismological Data Distribution SystemEIDA (European Integrated Data Archive).